Apparatus and method for intraoperative real-time tumour tissue discrimination

ABSTRACT

Apparatus for discriminating between tumour tissue and non-tumorous tissue in real-time, the apparatus comprising: a handheld bioimpedance probe having an elongate body and at least four stimulator electrodes mounted on a distal end of the elongate body, the electrodes being arranged to be held against a region of tissue in use; a current source configured to generate a stimulation current; a voltage sensor; a multiplexer coupled between the current source, the voltage sensor and the stimulator electrodes and configured to changeably switch between a plurality of switching configurations, wherein, in each switching configuration, a first two of the electrodes are connected to the current source, and a second two of the electrodes are connected to the voltage sensor, the electrodes that constitute the first two electrodes and the electrodes that constitute the second two electrodes changing from one switching configuration to the next; and processor-controlled circuitry configured to: control the switching configuration of the multiplexer; control the generation of the stimulation current by the current source and the application of the stimulation current to the first two electrodes of each switching configuration, such that, in use, the stimulation current flows through the tissue between the first two electrodes; control the measurement, by the voltage sensor, of the voltage between the second two electrodes of each switching configuration, across the tissue in use; determine, based on the applied current and the measured voltage for each switching configuration, a measure of relative impedance of the tissue for each switching configuration; and supply such impedance measurements as output data to a data analyser to enable real-time discrimination of the tissue to be performed, based on the impedance measurements. A handheld surgical tool is also provided, comprising an elongate body and an adjustable handle member that is pivotally coupled to the elongate body.

FIELD OF THE INVENTION

This invention relates to apparatus, and an associated method, forintraoperative real-time tumour tissue discrimination, to discriminatebetween tumour tissue and normal (non-tumorous) tissue. It isparticularly applicable for the identification of brain tumours,although it is by no means limited to such an application, and mayinstead be used to discriminate between tumour tissue and normal tissuein other parts of the human (or potentially animal) body.

BACKGROUND TO THE INVENTION

For effective diagnosis and treatment of cancers in the human (orpotentially animal) body, the correct identification of tumours, andaccurate discrimination between tumour tissue and normal (non-tumorous)tissue, is of great importance. Although the description that followsprimarily relates to the determination of brain tumours duringneurosurgery (i.e. neuro-oncology), the present disclosure is alsoapplicable to the identification of tumour tissue in other parts of thehuman (or animal) body.

With particular regard to brain tumours, despite several advances intheir management, tumours are either associated with high mortality andmorbidity (as with gliomas), or present significant challenges due todisruption of normal physiology following surgery (as with pituitarytumours). Surgical resection is a frequently-used treatment forextrinsic and intrinsic brain tumours, with key aims being to includethe most malignant tissue in the resected specimen, maximal resection,and avoiding or minimising removal of functional brain tissue [1].

Preservation of essential brain function combined with maximal, gentleand precise resection represents the best means of providing a surgicalcure. In this regard, gross total resection (GTR) (>90% ofmacroscopically visible tumour) is directly associated with improvedoutcomes (progression free survival, overall survival) and quality oflife. Further, supramaximal surgical resection (i.e. removing tissuebeyond the intended resection margin to account for microscopic tumourinvasion up to 2 cm beyond the ‘enhancing’ component of a tumour asvisualised on contrasted MRI imaging) has additionally been associatedwith improved outcomes. However this must be balanced with preservationof essential cognitive and homeostatic function. Indeed,surgically-acquired functional impairments are directly linked to poorerprognoses. Therefore, the corresponding challenge to maximal tumourresection in neuro-oncology surgery is the preservation of normalfunctioning tissue. This can be difficult, given that tumours may not beclearly distinguishable on the basis of visual inspection alone duringsurgery; tumours invade normal tissue at a microscopic level with even asmall volume of cells being relevant, involving normal tissue in a‘mosaic’ fashion. A further consideration is that brain tissue which hasbeen invaded by tumour may still have function. Therefore, identifyingand establishing the boundary of normal and abnormal brain tissue is afundamental goal of resective brain tumour surgery.

Tumour identification can in part be achieved through the use ofpre-operative neuroimaging, e.g. high-resolution MRI, which isintegrated with on-table ‘neuronavigation’— a type of intraoperativeanatomical ‘GPS’. However, a limitation of these approaches are thatthey are ‘macroscopic’. Further, they are usually acquiredpre-operatively or preoperatively, and as such are susceptible toreal-time distortions of the brain anatomy during surgical resection, asa result of tumour removal and brain ‘shift’.

There is, therefore, currently an unmet need in the field ofneuro-oncology for a simple, practical and robust means of on-table‘real-time’ differentiation of normal brain tissue from abnormal braintissue. More particularly, such a real-time intraoperative techniqueshould enable the detection of the surgical margin (i.e. distinguishingbetween healthy brain tissue and a tumour) during both resective andbiopsy procedures. Such a technique has the potential to improve thequality of neurosurgical treatment, optimising tumour identification andreducing excessive damage to healthy brain tissue [2]. This wouldultimately reduce the mortality rate associated with brain cancerrecurrence, along with financial and quality-of-life burdens to thepatient and healthcare provision linked to cancer recurrence. Real-timedifferentiation of brain tumour tissue from normal tissue facilitates(a) preservation of brain function by avoiding removal of normal orpredominantly normal brain tissue; and (b) increased precision andaccuracy in removing abnormal brain tissue, thereby facilitating GTR ofthe brain tumour.

Techniques which provide real-time visualisation during surgicalresection are the focus of significant investigation. Current approachesinclude hyperspectral imaging, confocal microscopy, intraoperativeultrasound-guided surgery (USS), and intraoperative Raman spectroscopy.The latter two technologies are currently in formal clinical use.Intraoperative USS is widely used but remains user dependent andvulnerable to difficulties in interpretation. This is particularly thecase when required to identify anything other than gross macroscopictissue abnormalities. Intraoperative Raman spectroscopy has recentlybeen translated into the neurosurgical operating theatre in the contextof a clinical trial with the promise of providing high resolution,microscopic identification of tumour cells [3].

Bioimpedance is one of the most promising means of evaluating thephysiological state of different tissue types, resulting from thebiological structure of tissues causing impedance differences.Bioimpedance techniques involve passing an electrical current throughbiological tissue while concurrently measuring the resistance to theflow of current produced by the tissue. It has been previously reported[4] that there are significant differences in bioimpedance of healthyand cancerous tissue in liver, prostate, breast, tongue and etc. in bothin-vivo and ex-vivo measurements [5]-[6]. However, existing bioimpedanceapparatus is primarily in the form of laboratory-based bench-topequipment, and is therefore not well suited to characterisingbioimpedance in real-time, intraoperatively, for the purpose of enablinga surgeon to differentiate normal brain tissue from abnormal braintissue (i.e. brain tumour tissue) during the course of surgery.

There is therefore a need for straightforward and effective bioimpedancecharacterisation apparatus that can conveniently be used by a surgeon toprovide real-time intraoperative bioimpedance-based information, toenable the surgeon to differentiate normal brain tissue from abnormalbrain tissue during the course of surgery, and thereby address at leastsome of the above problems. Other problems addressed by the presentdisclosure will become apparent from the description below and theaccompanying drawings.

A related challenge we address in the field of hand-held surgical toolsis the optimisation of the surgical handle to enhance frequently usedhand-grips. There are three cardinal hand positions when holding alinear pen-like instrument for artistic or surgical purposes. Theyinclude (1) a ‘pencil’ grip, with the first three fingers of the handforming a ‘tripod’ around the tool; (2) a ‘painter's’ grip, where oneend of the tool is held lightly primarily by the first two fingers; and(3) an ‘overhand extended’ grip stabilised by an extended index finger.Each of these grips offers specific improvements in precision, freedomof movement and stability relative to the other grips. Despite thelong-standing use of these different grips in a variety of fields, thereis an absence of a single dedicated tool handle which allows changes inposition to facilitate and fortify a specific grip.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is providedapparatus for discriminating between tumour tissue and non-tumoroustissue in real-time, as defined in claim 1 of the appended claims.

With the present invention, we target an existing intraoperativeclinical tool for the purpose of real-time tumour tissue identificationtaking advantage of its established use in the intraoperativeneurosurgical work-flow for tumour resection. Intraoperative directcortical stimulation is used in awake and asleep brain surgery toidentify functionally active brain tissue. The present invention expandson this principle, providing a handheld probe device to enable theapplication of bioimpedance for the purposes of real-timedifferentiation of brain tumour tissue from normal brain tissue.

More particularly, there is provided apparatus for discriminatingbetween tumour tissue and non-tumorous tissue in real-time, theapparatus comprising:

-   -   a handheld bioimpedance probe having an elongate body and at        least four stimulator electrodes mounted on a distal end of the        elongate body, the electrodes being arranged to be held against        a region of tissue in use;    -   a current source configured to generate a stimulation current;    -   a voltage sensor;    -   a multiplexer coupled between the current source, the voltage        sensor and the stimulator electrodes and configured to        changeably switch between a plurality of switching        configurations, wherein, in each switching configuration, a        first two of the electrodes are connected to the current source,        and a second two of the electrodes are connected to the voltage        sensor, the electrodes that constitute the first two electrodes        and the electrodes that constitute the second two electrodes        changing from one switching configuration to the next; and    -   processor-controlled circuitry configured to:        -   control the switching configuration of the multiplexer;        -   control the generation of the stimulation current by the            current source and the application of the stimulation            current to the first two electrodes of each switching            configuration, such that, in use, the stimulation current            flows through the tissue between the first two electrodes;        -   control the measurement, by the voltage sensor, of the            voltage between the second two electrodes of each switching            configuration, across the tissue in use;        -   determine, based on the applied current and the measured            voltage for each switching configuration, a measure of            relative impedance of the tissue for each switching            configuration; and        -   supply such impedance measurements as output data to a data            analyser to enable real-time discrimination of the tissue to            be performed, based on the impedance measurements.

The term “stimulation current” should be interpreted broadly, toencompass AC waveforms or potentially a DC signal; it may in practice beany arbitrary current.

By virtue of the bioimpedance probe being handheld and having anelongate body, this enables the probe to be conveniently used by asurgeon (or conceivably a robotic arm) to provide intraoperativebioimpedance-based information, preferably in a manner that does notobstruct the surgeon's view of the tissue region in question. Moreover,by virtue of having at least four stimulator electrodes and theaforementioned configuration and manner of operation of the multiplexer,impedance measurements can be obtained quickly and with a high degree ofprecision.

In certain embodiments the current source is a voltage controlledcurrent source, and the processor-controlled circuitry further comprisesa voltage waveform generator configured to generate a voltage waveformand to supply the voltage waveform to the current source. The currentsource may further comprise a high pass filter configured to remove DCoffset from the voltage waveform and to convert the voltage waveform tothe stimulation current. Such a high pass filter may not be required ifthe input of the voltage controlled current source is differential orbipolar.

Alternatively, a current waveform generator may be used, to generate acurrent waveform to directly drive the current source.

The voltage waveform generator or current waveform generator maycomprise a digital-to-analogue converter configured to receive apredefined stimulation waveform from which the voltage waveform orcurrent waveform is generated.

Alternatively, the voltage waveform generator or current waveformgenerator may comprise a Direct Digital Synthesis module configured toreceive a predefined stimulation waveform from which the voltagewaveform or current waveform is generated.

The stimulation waveform may be stored in the processor-controlledcircuitry.

Preferably the voltage waveform or current waveform comprises a mix of aplurality of different frequencies, thereby enabling the tissueimpedance at the different frequencies to be rapidly extracted usingFast Fourier Transform processing (or another appropriate technique).This greatly reduces the impedance measurement time compared to astandard chirp technique that would employ frequency sweeping, and alsoimproves measurement accuracy. Preferably the voltage waveform orcurrent waveform has substantially equal magnitude at each of theplurality of different frequencies.

Preferably the voltage sensor comprises an amplifier, such as aninstrumentation amplifier, or a differential amplifier.

Preferably the processor-controlled circuitry further comprises ananalogue-to-digital converter configured to receive and sample a voltagesignal from the amplifier and thereby generate digital voltage data.

For embodiments in which the voltage waveform comprises a mix of aplurality of different frequencies, the processor-controlled circuitrymay further comprise a Fast Fourier Transform processor configured toreceive the digital voltage data from the analogue-to-digital converter,and to convert time-domain data into frequency-domain data and therebyextract the instantaneous magnitude of the voltage data for eachfrequency in the stimulation waveform.

The multiplexer may be configured to cyclically switch between each ofthe plurality of switching configurations.

The processor-controlled circuitry may comprise a microcontroller.

In certain embodiments the voltage controlled current source and/or theamplifier are provided on a front-end printed circuit board orintegrated circuit within the probe.

The digital-to-analogue converter and/or the analogue-to-digitalconverter may be provided on a microcontroller unit (MCU) platform.

The data analyser may comprise a personal computer (PC), or anothersuitable device such as a tablet computer or smartphone.

In certain embodiments the electrodes may be spherical or hemispherical,and/or may be spring-loaded. Alternatively the electrodes may forexample be needle-shaped or pointed.

In certain embodiments the distal end of the elongate body may comprisea telescopic shaft on which the electrodes are mounted. Such anarrangement enables or facilitates endonasal access of the probe to thebrain.

The probe may further comprise an adjustable handle member at a proximalend of the elongate body. More particularly, the handle member may bepivotally coupled to the elongate body. This advantageously enables theprobe to be held more stably in the surgeon's hand, e.g. in either an‘overhand’ grip stabilised by an extended index finger (with the handleheld in the palm at an ‘angled’ setting) or in a ‘pencil’ grip.

In certain embodiments the handle member is pivotally and retractablycoupled to the elongate body by means of a linkage mechanism comprisinga first joint mounted on or in the handle member, a second joint mountedon or in the elongate body, and a connecting rod that extends from thefirst joint to the second joint and passes through at least one of thefirst and second joints to an adjustable extent, wherein at least one ofthe first and second joints comprises a ball-and-socket joint to enablerotation in three dimensions. For example, the second joint may comprisea ball-and-socket joint and the rod may extend through the second jointto an adjustable extent. Alternatively, or in addition, the first jointmay comprise a ball-and-socket joint and the rod may extend through thefirst joint to an adjustable extent.

Preferably, in the or each ball-and-socket joint, the surface of therespective ball part and/or the surface of the respective socket isadapted to hold the rotational position of the ball part relative to thesocket in a position as set by the user.

In certain embodiments the probe may further comprise an operationbutton mounted on the elongate body, operable to activate theprocessor-controlled circuitry.

The probe may further comprise depressions on the elongate body, forreceiving the user's fingertips in use, in order to further stabilisethe instrument.

In certain embodiments the probe may be wireless, to facilitateunencumbered manipulation of the probe by the surgeon.

In certain embodiments the probe may further comprise a pressure sensor,for measuring the contact pressure between the electrodes and the tissuein use.

In certain embodiments the probe may further comprise a blood oxygensensor at the distal end of the elongate body, for measuring the bloodoxygen level of the tissue in use.

In certain embodiments the probe may further comprise an accelerometeror inertial sensor to sense the angle of inclination of the probe.

According to a second aspect of the present invention there is provideda handheld surgical tool comprising an elongate body and an adjustablehandle member that is pivotally coupled to the elongate body.Application of the adjustable handle member is by no means limited tothe present bioimpedance probe; the principles of the adjustable handlemember are also applicable to other surgical tools having an elongatebody for which a more stable hold is desired. Optional features of theadjustable handle member are as outlined above in relation to the firstaspect of the invention.

According to a third aspect of the present invention there is provided amethod of discriminating between tumour tissue and non-tumorous tissuein real-time, using the apparatus according to the first aspect of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, and with reference to the drawings in which:

FIGS. 1 a and 1 b illustrate side views of a handheld bioimpedancemeasurement probe having an adjustable (pivotable and retractable)handle member, an elongate shaft-like body, and a stimulator end (whichmay optionally be telescopic) having a plurality of stimulationelectrodes;

FIG. 2 a illustrates another side view of the bioimpedance measurementprobe;

FIG. 2 b illustrates an enlargement of region A of FIG. 2 a , showing aclose-up of the stimulator end and four stimulation electrodes;

FIGS. 3 a, 3 b and 3 c illustrate, respectively, a top view, side viewand end-on view of the bioimpedance measurement probe;

FIG. 4 a illustrates another side view of the bioimpedance probe, whichincludes an operation button and finger-grip depressions;

FIG. 4 b illustrates an enlargement of region A of FIG. 4 a , showing aclose-up of the operation button and finger-grip depressions;

FIGS. 5 a and 5 b illustrate cross-sections of a linkage mechanism forpivotally and retractably coupling the handle member to the elongatebody of the bioimpedance measurement probe, in retracted and extendedconfigurations respectively;

FIGS. 6 a to 6 d illustrate further cross-sections of the linkagemechanism of FIGS. 5 a and 5 b , in a variety of configurations;

FIG. 7 illustrates a variant of the adjustable handle and pivotallinkage mechanism of FIGS. 5 a and 5 b;

FIG. 8 illustrates possible angular positions into which the handle ofFIG. 7 may be adjustably set, by means of the pivotal linkage mechanism;

FIGS. 9 a, 9 b and 9 c illustrate further possible positions into whichthe handle of FIG. 7 may be adjustably set, by means of the pivotallinkage mechanism;

FIG. 10 illustrates a block diagram of an example bioimpedancecharacterisation system for use with, or incorporating, the abovebioimpedance measurement probe;

FIG. 11 illustrates example front-end analogue circuit schematics forthe system of FIG. 10 , including a voltage controlled current source, avoltage buffer, an instrumentation amplifier, and a multiplexer to whichthe stimulation electrodes of the bioimpedance measurement probe areconnected;

FIG. 12 illustrates an electrode switching sequence in respect of abioimpedance measurement probe having four stimulation electrodes, inwhich four different electrode configurations are cycled through;

FIG. 13 illustrates a variant of the electrode switching sequence ofFIG. 12 , again in respect of a bioimpedance measurement probe havingfour stimulation electrodes, but in which six different electrodeconfigurations are cycled through;

FIG. 14 illustrates examples of how the aforementioned probeconfiguration employing four-electrode measurement can be extended tomore electrodes;

FIG. 15 schematically illustrates a multiplexer switching arrangementfor supplying a current to a selected pair of stimulation electrodeswhen cycling though a series of electrode configurations;

FIG. 16 illustrates a voltage waveform and a corresponding FFT frequencyresponse output, showing that the voltage waveform comprises multiplefrequencies;

FIG. 17 is a flow diagram in respect of the operation of thebioimpedance characterisation system and measurement probe;

FIG. 18 a illustrates a linearity characterisation of an exampleimplementation of the bioimpedance characterisation system, from 0.2Ω to500Ω;

FIG. 18 b illustrates noise analysis of the bioimpedancecharacterisation system on a 25Ω discrete resistor with a samplingfrequency of 192 kSample/s;

FIG. 19 illustrates reconstructed resistance mapping in respect of aregion of metal surrounded with saline solution, performed using (a) anAgilent E4980A Precision LCR meter, and (b) a bioimpedancecharacterisation system and measurement probe according to the exampleimplementation of the invention (as per the described Example 1);

FIG. 20 illustrates four measured voltage waveforms (as per thedescribed Example 2);

FIG. 21 illustrates the FFT frequency response corresponding to each ofthe waveforms of FIG. 20 ;

FIG. 22 illustrates the detection of a biological tissue region withhigher bioimpedance relative to a tissue region of lower bioimpedance;

FIG. 23 illustrates four measured voltage waveforms (as per thedescribed Example 3);

FIG. 24 illustrates the FFT frequency response corresponding to each ofthe waveforms of FIG. 23 ;

FIG. 25 illustrates the detection of a biological tissue region withhigher bioimpedance relative to a tissue region of lower bioimpedance;and

FIG. 26 illustrates (a) a piece of rib-eye steak (acting as a biologicalsample), and (b) reconstructed impedance mapping of the different tissuetypes (fat vs muscle fibre) across the piece of rib-eye steak, performedusing the abovementioned example implementation of the invention (as perthe described Example 4).

In the figures, like elements are indicated by like reference numeralsthroughout.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present embodiments represent the best ways known to the Applicantof putting the invention into practice. However, they are not the onlyways in which this can be achieved.

The present disclosure provides apparatus for discriminating betweentumour tissue and non-tumorous tissue in real-time using bioimpedancemeasurements.

More particularly, through measuring the electrical properties ofbiological tissue of the brain tumour, we are able to identify adifference between normal and abnormal brain tissues. Further, impedancemeasurements are expected to enable differentiation between lessaggressive and more aggressive tumour tissue. By evaluating thesebioimpedance properties intraoperatively, clinically relevantinformation regarding surgical margin can be established in real-time[7].

Bioimpedance Probe—Physical Architecture

With reference initially to FIGS. 1 a , 1 b, 2 a, 2 b, 3 a, 3 b, 3 c, 4a and 4 b, the present apparatus comprises a handheld bioimpedance probe10 having an elongate body 14, at least four stimulator electrodes 20a-20 d mounted on a distal end of the elongate body 14, and, optionally,an adjustable handle member 12 (that will be described in greater detailbelow with reference to FIGS. 5 a to 9 c ). In various embodiments, theelectrodes 20 a-20 d may be relatively long (e.g. pin-like,needle-shaped or pointed) or relatively short (e.g. stubby), and may bespherical or hemispherical in shape. In use, the tips of the electrodes20 a-20 d are held against a region of tissue that is to be investigatedfor the presence of tumours, for the purpose of discriminating betweentumour tissue and normal (non-tumorous) tissue. Optionally butadvantageously, the electrodes 20 a-20 d may be spring-loaded so as tocushion their contact with the tissue being tested, and reduce theextent to which they press into the tissue.

In the illustrated embodiment the stimulator electrodes 20 a-20 d aremounted at the end of an optional telescopic shaft 18, that isextendable from, and retractable into, a cylindrical sleeve 16 at thedistal end of the body 14. The length of the telescopic shaft 18 thatprotrudes from the cylindrical sleeve 16 can be lengthened or shortenedand then fixed, to produce a desired case-specific or surgeon-specificlength, thereby facilitating user-optimised application. An adjustmentmechanism for adjusting and locking (or unlocking) the protruding lengthof the telescopic shaft 18 may be provided, as those skilled in the artwill appreciate. The telescopic end of the probe 10 enables orfacilitates endonasal access to the brain; for this the entire probe maybe of a more elongated structure.

The optional adjustable handle 12 may incorporate, or be made from, apadded or malleable material, and can be placed in the surgeon's palm,creating an ‘angled grip’ of the probe 10. Alternatively, the adjustablehandle 12 can be positioned above the first web space of the hand,thereby creating a ‘pencil grip’ of the probe 10. In either case, thishelps the surgeon achieve greater control and precision grip of theprobe 10.

More particularly, the adjustable handle 12 may be bent down, at anangle from the elongate body 14, to fit into the user's palm, with theuser's fingers forming an encircling grip around the back of theinstrument. The angulation of the handle 12 with respect to the body 14produces specific utility as an ‘angled’ grip. Alternatively the handle12 can be brought up and locked into place, in line with the body 14,enabling a ‘pencil’ grip.

An operation button 24 (shown in close-up in FIG. 4 b ) is mounted onthe elongate body 14, near to the finger depressions 26, for operationby the surgeon's index finger. Pressing the button 24 causes the probe10 to operate, and releasing the button 24 causes operation of the probeto stop.

Bilateral finger depressions 26 are provided on the elongate body 14,either side of the operation button 24, to enable further stabilisationof the instrument, particularly when in the ‘angled grip’ position(which is expected to have specific utility for endonasal use).

The overall design of the elongate handheld probe 10 is such that it islow-profile and light in weight, rendering it suitable for use indelicate microsurgical procedures, or minimally-invasive brain surgery(e.g. microscope-based, endonasal or endoscopic surgery), to provide thesurgeon with a real-time ‘look-ahead’ differentiation between abnormaland normal brain tissue.

Adjustable Handle

As mentioned above, the probe 10 may be provided with an adjustablehandle member 12, to enable the probe 10 to be held more stably in thesurgeon's hand. In the presently-preferred embodiments the handle member12 is pivotally and retractably coupled to the elongate body 14 of theprobe by means of a linkage mechanism.

FIGS. 5 a and 5 b illustrate cross-sections of the linkage mechanism forpivotally and retractably coupling the handle member 12 to the elongatebody 14 of the probe 10, in retracted and extended configurationsrespectively.

The linkage mechanism comprises a first joint (22 a, 22 b) mounted on orin the handle member 12, a second joint (22 c, 22 d) mounted on or inthe elongate body 14, and a connecting rod 22 that extends from thefirst joint to the second joint. In the illustrated embodiment the firstjoint is a ball-and-socket joint comprising a ball 22 a on a first endof the rod 22, and a socket 22 b in the handle 12 into which the ball 22a locates. Similarly, the second joint is a ball-and-socket jointcomprising a ball 22 c on the second end of the rod 22, and a socket 22d in the body 14 into which the ball 22 c locates. At least one of thefirst and second joints (in the illustrated case, the second joint) isrotatable.

In each ball-and-socket joint, the surface properties between the ballpart and its respective socket are preferably such as to enable therotational position of the ball relative to the socket to be ‘fixed’ bythe user as desired. For example, dimples/pimples or some other detentmechanism may be incorporated on the outer surface of the ball and/orthe inner surface of the socket. Alternatively the ball-and-socket jointmay employ a snug/tight friction-based fit, or some other kind of stickyinterface between the ball and the socket.

To permit extension and retraction of the handle 12 relative to the body14, the rod 22 passes through at least one of the first and secondjoints (in the illustrated case, the second joint and not the first) toan adjustable extent. Accordingly, a channel 28 is provided within thebody 14 to accommodate the rod 22 when in the retracted state. The firstend of the rod 22 is fixedly attached to the ball 22 a of the firstjoint, whereas the second end of the rod 22 is non-fixedly (e.g.slidingly) coupled to the ball 22 c of the second joint.

The second end of the rod 22 is provided with a gripping region 22 ethat, at the point of maximum extension, engages with agripping/restraining collar 22 f mounted on the ball 22 c and preventsthe rod 22 from separating from the ball 22 c.

FIGS. 6 a to 6 d illustrate further cross-sections of the linkagemechanism of FIGS. 5 a and 5 b , in a variety of configurations. Moreparticularly, FIG. 6 a shows the handle 12 fully retracted, close to thebody 14, with the rod 22 accommodated in the channel 28 within the body14. FIG. 6 b shows the handle 12 fully extended, away from the body 14,in a linear manner. FIG. 6 c shows the extended handle 12 angled to oneside by rotation of the ball 22 c within the socket 22 d in onedirection, and FIG. 6 d shows the extended handle 12 angled to the otherside by rotation of the ball 22 c within the socket 22 d in the oppositedirection.

FIG. 7 illustrates a variant of the adjustable handle and pivotallinkage mechanism of the bioimpedance measurement probe. In thisvariant, in the two ball-and-socket joints, both the balls 22 a and 22 care rotatable relative to their respective sockets 22 b and 22 d (thelatter not being visible in the figure). The connecting rod 22 may againbe telescopic.

FIG. 8 illustrates possible angular positions into which the handle 12of FIG. 7 may be adjustably set, by means of the pivotal linkagemechanism, by rotation of the ball 22 a within the socket 22 b. Thedouble-headed curved arrow represents angular adjustment of the handle12 between the two angular positions illustrated.

FIGS. 9 a, 9 b and 9 c illustrate possible extended and retractedpositions into which the handle of FIG. 7 may be adjustably set, bymeans of the pivotal linkage mechanism. More particularly, FIG. 9 bshows the handle 12 in an extended position relative to the body 14,whereas FIG. 9 c shows the handle 12 in a retracted position relative tothe body 14. FIG. 9 a shows both the extended and retracted positionsoverlaid on one another.

It will be appreciated that application of the adjustable handle member12 is by no means limited to the present bioimpedance probe 10, and thatthe principles of the adjustable handle member 12 of FIGS. 5 a to 9 care also applicable to other surgical tools having an elongate body, forwhich a more stable hold is desired, such as a needle driver or scalpelblade.

Bioimpedance Characterisation System Electronics

We have identified the essential requirements for an intraoperativeimpedance probing system. To prove the concept, an example PCB-basedsystem has been designed and implemented with an on-board current sourcegenerator and voltage amplification circuits. A tetrapolar impedanceprobe based on four electrodes 20 a-20 d has been used and impedancemeasurements across electrode pairs have been characterised via I-V(current-voltage) measurement using a multitone sinusoidal currentwaveform. Measured results have then been processed by a microcontrollerand host PC platform to identify the impedance values and reconstruct animpedance map in respect of the test samples. These results have beencompared with a commercially-available Agilent E4980A Precision LCRinstrument to benchmark performance.

With reference initially to FIG. 10 , in a general sense the presentapparatus comprises (in addition to a probe 10 as described above,having at least four stimulator electrodes 20 a-20 d at its distal end):a current source 37 configured to generate a stimulation current; avoltage sensor (e.g. instrumentation amplifier) 36; and a multiplexer 39coupled between the current source 37, the voltage sensor 36 and thestimulator electrodes 20 a-20 d and configured to changeably (preferablycyclically) switch between a plurality of switching configurations, suchas those described below with reference to FIGS. 12 and 13 .

In each switching configuration, a first two of the electrodes areconnected to the current source 37, and a second two of the electrodesare connected to the voltage sensor 36, the electrodes that constitutethe first two electrodes and the electrodes that constitute the secondtwo electrodes rapidly changing from one switching configuration to thenext.

Processor-controlled circuitry is also provided, configured to:

-   -   control the switching configuration of the multiplexer 39 (by        application of a control signal to the multiplexer);    -   control the generation of the stimulation current by the current        source 37 and the application of the stimulation current to the        first two electrodes of each switching configuration, such that,        in use, the stimulation current flows through the tissue between        the first two electrodes;    -   control the measurement, by the voltage sensor 36, of the        voltage between the second two electrodes of each switching        configuration, across the tissue in use;    -   determine, based on the applied current and the measured voltage        for each switching configuration, a measure of relative        impedance of the tissue for each switching configuration; and    -   supply such impedance measurements as output data to a data        analyser to enable real-time discrimination of the tissue to be        performed, based on the impedance measurements.

The impedance of tissue cell is well studied for cellular processes orbrain tissue [8]. However, the distribution of impedance of brain tumouris not conclusive. A recent study stated the average impedancemeningiomas, low-grade gliomas, and high-grade gliomas are 530 Ω-cm, 160Ω-cm, and 498 Ω-cm respectively [8]. Therefore, we have determined thatthe target impedance range should ideally cover 100 Ω-cm to 600 Ω-cm.

The present four-electrode measurement method is used due to it notbeing affected by polarisation (unlike a two-electrode method, whichwould be affected by polarisation). For safety reasons, the stimulationcurrent driving the electrodes 20 a-20 d should of course be incompliance with appropriate medical device regulations, and is typicallyless than 10 μA. Considering the impedance of normal and cancerous braintissues, the voltage level received at the sensing electrodes istypically in the range of a few millivolts, depending on the stimulationcurrent used and the spacing of the electrodes.

To enable real-time intraoperative impedance characterisation, theprocessing time should be minimised. Therefore the control electronics(e.g. microcontroller unit (MCU) 31) should be capable of converting theanalogue signal if an on-board analogue-to-digital converter 32 is used,and extracting frequency domain signals by using Fast Fourier Transform(FFT) or envelope detection. As saline solution has to be poured overthe cortex of the brain frequently to avoid drying, an analoguemultiplexer 39 is preferably used to switch between different measuringconfigurations to ensure rapid measurement time and consistentmeasurements recorded over each configuration.

System Architecture

In more detail, a block diagram of the electronics system of our exampleimplementation is shown in FIG. 10 . It consists of four main parts:

1) A compact handheld probe (probe 10 described above) with multi-poleelectrodes 20 a-20 d to perform versatile impedance characterisationconfiguration.

2) A front-end printed circuit board 35 (or integrated circuit), whichmay be incorporated within the probe 10, or provided in a separateinterface unit to which the probe 10 (specifically the electrodes 20a-20 d thereof) is connected. In this example the front-end board 35includes a voltage controlled current source 37 to generate thestimulation current; an instrumentation amplifier 36 to sense thevoltage signal; and a multiplexer array 39 for switching the currentsource 37 and the instrumentation amplifier 36 between electrodes. Asillustrated, a Direct Digital Synthesis (DDS) module 38 may also beprovided. A standalone ADC or DAC may be added to alleviate theprocessing burden in the microcontroller unit (MCU) 31. However, asmentioned below, in other embodiments the current source may directlygenerate a stimulation current for driving the electrodes 20 a-20 d,with the current source being driven by a current waveform generator(e.g. a current DAC).

3) An MCU platform 31 to control the standalone waveform generator orADC, and pre-process the data. This may also be incorporated within theprobe 10, or provided in a separate interface unit to which the probe 10(specifically the electrodes 20 a-20 d thereof) is connected. In thisexample the MCU platform 31 includes a digital-to-analogue converter(DAC) 33 which is configured to generate a voltage waveform and tosupply the voltage waveform to the voltage controlled current source 37;and an analogue-to-digital converter (ADC) 32 configured to receive andsample a voltage signal from the instrumentation amplifier 36 andthereby generate digital voltage data. The MCU platform also includes amodule 34 comprising a general purpose input/output (GPIO), a serialperipheral interface (SPI) and a clock (CLK) to interface with the DDSmodule 38.

4) A back-end host computer 30 (or other processing/visualisationdevice, such as, but not limited to, a tablet computer or smartphone) toreconstruct the data for visual display. In alternative embodiments thisneed not provide visualisation, and could just provide an indicator(e.g. an audible notification) instead.

A predefined stimulation waveform is stored in the MCU 31 and sent tothe DAC 33 or the Direct Digital Synthesis (DDS) waveform generator 38,to cause the voltage waveform to be generated. The generated voltagewaveform is then converted to current source with required slew rate andbandwidth. This differential current is directed to the target electrodepair in the probe 10 by the multiplexer 39. The other pair of electrodesin the probe 10 are set to sense the voltage induced by the impedance ofthe tissue. This voltage signal is amplified by the instrumentationamplifier 36 and converted into the digital domain by the ADC 32. Thenthe measured waveform is processed using FFT to obtain the impedancemeasurement at each frequency of interest. The impedance measurements ofeach different connection configuration (e.g. as shown in FIG. 12 orFIG. 13 ) are compared with each other to identify the existence of amargin within the four electrodes, and which pair of electrodes are theclosest to the margin. In our example implementation, the overallprocessing time is under 73 ms for 4096 data points in eachconfiguration.

Circuit Implementation

FIG. 11 shows example front-end analogue circuit schematics comprising:the voltage controlled current source 37; a voltage buffer 40; theinstrumentation amplifier 36; and the multiplexer 39.

In the illustrated example, in the voltage controlled current source 37,a passive first order high pass filter (R₁, C₁) is provided to removethe DC offset of the generated waveform. A buffered differentialamplifier and integrator fix the voltage across the resistor R_(a) withregard to the input voltage. This generates a current flowing fromI_(op) to I_(on) accordingly. The return current is sunk or sourced byan op-amp in the voltage buffer 40 to provide a low impedance currentpath and allow a bias voltage to be adjusted.

To explain this further, as the voltage waveform is generated witheither the DDS module 38 or the DAC 33, the voltage will have a range 0Vto the maximum output voltage of the DDS 38 or DAC 33. (At thisjuncture, it should be noted that only one of the DDS 38 or DAC 33 maybe present to generate the voltage waveform, even though both areillustrated in FIG. 10 .) The high pass filter formed by R₁ and C₁ istherefore used to remove the DC offset (mean of waveform). The remainingsignal is passed further into the voltage-controlled current source(VCCS) 37 to convert the voltage waveform into a current waveform.

In the illustrated example, a multi op-amp topology is used to improvethe overall performance of the VCCS 37 by taking advantage of op-ampsoptimised in specific areas for each stage. The resulting VCCS resultsin a higher bandwidth current source compared to a Howland current pump,for example. Other VCCS topologies would work as well. The voltage tocurrent ratio is set by resistor R_(a). The amplifier on theright-hand-side of the illustrated VCCS 37 is a unity-gain amplifier; itoutputs the voltage at its positive terminal with virtually zero leakagecurrent, ensuring all of the current going through resistor R a will gointo the multiplex (MUX) 39. The middle amplifier of the illustratedVCCS 37 outputs the voltage difference across resistor R^(a). The leftamplifier of the illustrated VCCS 37 completes the feedback loop andgenerates the required current for the voltage to current conversion.

In other words, in the illustrated example, the current source 37 is avoltage controlled current source. The processor-controlled circuitrycomprises a voltage waveform generator configured to generate a voltagewaveform and to supply the voltage waveform to the voltage controlledcurrent source 37. The voltage waveform generator may comprise adigital-to-analogue converter 33 configured to receive a predefinedstimulation waveform from which the voltage waveform is generated.Alternatively, the voltage waveform generator may comprise a DirectDigital Synthesis module 38, also configured to receive a predefinedstimulation waveform from which the voltage waveform is generated. Thevoltage controlled current source 37 comprises a high pass filterconfigured to remove DC offset from the voltage waveform and to convertthe voltage waveform to the stimulation current that is applied to thestimulation electrodes via the multiplexer 39.

The amplifier in the voltage buffer 40 offers a low impedance path forthe current injected from I_(op) to return to the system, with theoption of applying a DC voltage to further reduce DC offset on theexcitation waveform (inject signal). At the same time, such an amplifiermay track the bias voltage, and control the current source to compensatefor the bias voltage.

The instrumentation amplifier 36 is used to measure the potentialdifference between the two sensing electrodes which are set for thatpurpose, at that moment in time, by the analogue multiplexer 39. Moreparticularly, the instrumentation amplifier 36 amplifies the voltagedifference between V_(in) and V_(ip). The instrumentation amplifier 36does not have to be an off-the-shelf single package IC, and it could beformed by a combination of amplifiers to create equivalent voltageamplification or using application-specific IC.

The multiplexer 39 changeably defines each instantaneous configurationof the electrodes, and redirects I_(op), I_(on), V_(in), and V_(ip) tothe designated electrodes according to the selected electrodeconfiguration at that moment in time.

Electrode Switching Configurations

FIG. 12 shows, by way of example, four tetrapolar electrode switchingconfigurations (A, B, C and D) sequentially constructed by the analoguemultiplexer 39. In our practical implementation, the apparatus measuresthe impedance in each configuration in a time frame of under 22 ms, andthe implemented analogue front-end circuit may have a bandwidth of up to1 MHz. The electrodes 20 a-20 d are arranged in a square configurationat the distal tip of the probe 10.

In electrode switching configuration A, the stimulation current I₁ isapplied from electrode 20 a to electrode 20 b, and the correspondingvoltage V₁ is measured between electrodes 20 c and 20 d.

Next, in electrode switching configuration B, the stimulation current I₂is applied from electrode 20 d to electrode 20 a, and the correspondingvoltage V₂ is measured between electrodes 20 b and 20 c.

Then, in electrode switching configuration C, the stimulation current I₃is applied from electrode 20 c to electrode 20 d, and the correspondingvoltage V₃ is measured between electrodes 20 a and 20 b.

Then, in electrode switching configuration D, the stimulation current I₄is applied from electrode 20 b to electrode 20 c, and the correspondingvoltage V₄ is measured between electrodes 20 d and 20 a.

The sequence of switching configurations A-D may be repeated by themultiplexer 39 in a cyclic manner.

FIG. 13 shows how the number of different configurations with afour-electrode measurement can be extended to six whilst maintainingfour electrodes, by adding further switching configurations E and F tothe above-described sequence of switching configurations A-D.

In electrode switching configuration E, the stimulation current I₅ isapplied from electrode 20 a to electrode 20 c, and the correspondingvoltage V₅ is measured between electrodes 20 b and 20 d.

In electrode switching configuration F, the stimulation current I₆ isapplied from electrode 20 b to electrode 20 d, and the correspondingvoltage V₆ is measured between electrodes 20 a and 20 c.

The sequence of switching configurations A-F may be repeated by themultiplexer 39 in a cyclic manner.

As those skilled in the art will appreciate, more than four stimulatorelectrodes may be used. To illustrate this, FIG. 14 provides examples((a)-(d)) of how the aforementioned probe configuration employingfour-electrode measurement can be extended to more electrodes (with eachcircle in the figure representing a respective electrode).

More particularly, using the understanding from the initial tetrapolarconfiguration probe, the number of electrodes can be increased, and amore sophisticated electrode arrangement can be formed. FIG. 14 providesexamples of how the scale and complexity of the probe can be extended.With 12 electrodes, multiple tetrapolar configurations can be formedbetween the electrodes, greatly increasing the resolution of themeasurements. Margin analysis can be performed using similar electrodeplacement to estimate how the margin passes through the area covered bythe electrodes.

FIG. 15 schematically illustrates a multiplexer switching arrangementfor supplying a current to a selected pair of stimulation electrodes (inthis case, “Electrode A” and “Electrode B”) when cycling though a seriesof electrode configurations. Each electrode can be switched to any ofthe following by operation of the multiplexer 39:

-   -   “Current Output”—to supply the stimulation current to the tissue    -   “Current Return”—to receive the stimulation current from the        tissue    -   “Voltage−” and “Voltage+”—the electrodes between which the        corresponding voltage is measured

Waveform Characteristics

Advantageously, in the presently-preferred embodiments, the voltagewaveform that is generated and supplied to the voltage controlledcurrent source 37 (i.e. by the DAC 33 or DDS 38) comprises a mix of aplurality of different frequencies. This is illustrated in FIG. 16 . Theupper trace shows an example voltage waveform, whereas the lower traceshows a corresponding FFT frequency response output, showing that thevoltage waveform comprises multiple frequencies.

As mentioned above, the predefined voltage waveform is converted to thestimulus current by the VCCS 37. In the illustrated example the waveformis designed to have substantially equal magnitude at the differentfrequencies of 1 kHz, 3 kHz, 5 kHz, 16 kHz, 24 kHz, 32 kHz, 48 kHz, 60kHz, and 80 kHz, sampled at a frequency of 192 kHz. The number ofsinusoidal waveforms and their frequencies is not fixed, but the maximummeasurable sinusoidal frequency will need to be half of the samplingfrequency (Nyquist sampling criterion). Advantageously a multi-frequencywaveform is used such that multiple frequencies' impedance can berapidly extracted using FFT, greatly reducing the measurement timecompared to a standard chirp technique. This is because a standard chirptechnique would require frequency sweeping to take place. However, thepresent technique employs multiple frequencies simultaneously, enablingthe impedance result to be rapidly obtained, after only a small number(e.g. a few) of electrode switching cycles. The above frequencies havebeen chosen to keep the overall amplitude of the waveform low tomaximise the dynamic range of the system and with a low slew rate toease requirements for electronic components. The chosen frequency rangemay be limited due to component limitations. In addition, the phase ofan individual sinusoidal waveform can be changed to further reduce theoverall amplitude of the waveform.

In our example implementation, we used 4096 samples due to resourceconstraints by the microcontroller architecture; however, any number ofsamples would work. A higher number of samples would increase thefrequency resolution of the calculated impedance; a lower number ofsamples would reduce the total measurement time. The predefined waveformmay be repeated multiple times in the measurement period, such that thecalculated impedance would be an averaged overall repetition of thewaveform, resulting in lower noise measurement.

Operating Method

FIG. 17 provides a flow diagram illustrating the operation of theabove-described bioimpedance characterisation system and measurementprobe. The constituent steps are as follows:

Step S1: Configure the switching configuration of the multiplexer 39 forthe designated electrode configuration for that moment in time (e.g. oneof configurations A to D as shown in FIG. 12 ), by applying a controlsignal to the multiplexer 39.

Step S2: Generate the voltage waveform through the DAC 33 or DDS 38.

Step S3: Pass the voltage waveform into the high pass filter to removeDC offset, and convert to stimulation current waveform (excitationsignal) in the voltage controlled current source 37.

Step S4: Apply the stimulation current waveform (excitation signal) tothe tissue via the multiplexer, using one electrode for currentinjection, and another electrode as the current return path.

Step S5: Measure voltage between the other two electrodes usinginstrumentation amplifier 36 (or differential amplifier).

Step S6: Sample the measured voltage signal with the ADC 32.

Step S7: If measurements have been performed on all switchingconfigurations, continue to step S8, otherwise, repeat the process fromstep S1, reconfiguring the electrode configuration to the next in thesequence (e.g. switching from configuration A to configuration B; orfrom B to C; or from C to D; or from D to A, until measurements havebeen performed at least once on each of the switching configurations).

Step S8: Convert the data type of the sampled data into floating-point(data type for running FFT) and run FFT (Fast Fourier Transform). Anysuitable algorithm can be used to convert time-domain data into thefrequency domain, or other means may be used to extract theinstantaneous magnitude across the frequency through time (e.g. wavelettransform).

Step S9: Calculate the relative impedance of the tissue in eachconfiguration using suitable algorithms (e.g. application of ohm's law,machine learning, networks).

Steps S10 & S11: Data processing and results analysis, performed by PC30. Algorithms can be applied on the data generated in step S9 toperform margin analysis, tissue identification, physiological stateestimation, etc., according to the surgeon's requirements.

Experimental Demonstrations Example 1— Test Using Metal Plate

A saline testing setup was assembled with our example implementation ofthe present device, using a 3-axis cramp to hold the probe over thetesting area. A 1 cm×1 cm piece of metal was placed at the centre of theglass container with 1 cm deep saline solution. A set of 6-by-6impedance measurements were recorded using the electrodes with a 2.54 mmspacing. The electrodes used were gold-plated spring-loaded pins.

The implemented device was calibrated with a 25Ω resistor with 0.5%tolerance. The typical error of the device is below 2% with a resolutionof 1Ω. FIG. 18 a shows the linearity of the device, comparing measuredimpedance with actual impedance in respect of impedance values from 0.2Ωto 500Ω, and FIG. 18 b shows the noise analysis on a 25Ω resistor. FromFIG. 18 a , the measurements on different resistor values have shown thedevice has a linearity of 0.1%. The error increases as the impedanceunder test decreases, as the signal approaches the noise floor.

FIG. 19 shows the reconstructed resistance mapping, across and aroundthe 1 cm×1 cm piece of metal, using (a) a commercially-available AgilentE4980A Precision LCR meter, and (b) the implemented device,respectively. The dark-shaded low impedance area denotes the metal 50 atthe centre, surrounded with light-shaded (relatively high impedance)saline solution 52. Both the Agilent E4980A LCR meter and theimplemented device successfully detected the location and the margin ofthe metal.

Example 2

FIG. 20 illustrates four voltage waveforms (as measured by theinstrumentation amplifier 36 and sampled by the ADC 32) measured from aregion of biological tissue, and FIG. 21 illustrates the respective FFTfrequency responses, for each of the four electrode switchingconfigurations A-D shown in FIG. 12 .

As illustrated, the bottom left electrode is denoted 20 a, the bottomright electrode is 20 b, the top right electrode is 20 c, and the topleft electrode is 20 d. As in FIG. 12 , in configuration C of FIG. 20the current was injected at electrode 20 c and returned via electrode 20d, and the corresponding voltage was measured across electrodes 20 a and20 b. From FIG. 20 it can be seen that the measured voltage inconfiguration C, across electrodes 20 a and 20 b, is the highestcompared to other configurations.

Then, in configuration D of FIG. 20 , the current was injected atelectrode 20 b and returned via electrode 20 c, and the correspondingvoltage was measured across electrodes 20 a and 20 d. It can be seenthat the measured voltage was higher than the voltages observed inconfigurations A and B, although not as high as in configuration C.

These voltage measurements can be interpreted as meaning that electrode20 c is on an area with higher bioimpedance compared to thesurroundings, but the area of higher bioimpedance does not extend to anyother electrodes. Such an arrangement is sketched in FIG. 22 , whereinthe shaded area 60 (in which electrode 20 c is located) representstissue with higher bioimpedance (e.g. different physiological statetissues), and the unshaded area 62 (in which electrodes 20 a, and 20 dare located) represents tissues with lower bioimpedance. The area 60 canbe irregular, and the bioimpedance need not be constant across one area.This illustrates that, in this example, the tissue under electrode 20 cis different from that under the other electrodes, and the differencesdo not reach any of the other electrodes.

Example 3

From a different region of biological tissue to that of Example 2, FIG.23 illustrates another four measured voltage waveforms (as measured bythe instrumentation amplifier 36 and sampled by the ADC 32), and FIG. 24illustrates the respective FFT frequency responses, for each of the fourelectrode switching configurations A-D shown in FIG. 12 .

From FIG. 23 it can be seen that the measured voltage in configurationsA and C are higher than those measured in configurations B and D. Thesevoltage measurements can be interpreted as meaning that there is atissue margin crossing the probe, such that electrodes 20 a and 20 d areon one side of the margin, and electrodes 20 b and 20 c are on the otherside of the margin. Such an arrangement is sketched in FIG. 25 , whereinthe shaded area 60 (in which electrodes 20 a and 2 d are located)represents tissue with higher bioimpedance (e.g. different physiologicalstate tissues), and the unshaded area 62 (in which electrodes 20 b and 2c are located) represents tissues with lower bioimpedance.

Example 4— Test on Rib-Eye Steak

By scanning the probe across a tissue sample and taking impedancemeasurements at each position using each of the four electrodeconfigurations, the present technique may be used to calculate thebioimpedance under the probe at each position across the sample, and animpedance map can in turn be generated. (Even if just a singleconfiguration were to be used in each position, an impedance map couldstill be achieved, although this would be of courser quality, and somemeasurements could be saturated, giving erroneous results.) Using thepresent four-configuration measurement technique at each position acrossthe sample therefore provides better macro scale robustness andresolution.

To illustrate this, the same practical implementation as used in Example1 was used with the piece of metal replaced by a portion of rib-eyesteak, as shown in image (a) of FIG. 26 . Image (b) of FIG. 26 shows areconstructed impedance map obtained using the present device. The highimpedance area (having lighter shading) mainly represents the fat on thesteak. The map illustrates the margin of the fat and muscle fibre withinthe state (the muscle fibre being darker shaded, having relatively lowimpedance). This demonstrates that the present apparatus is able todiscriminate between different types of tissue using bioimpedancemeasurements.

Conclusion of Experimental Demonstrations

In this work, a bioimpedance measuring device has been successfullyimplemented for performing real-time tissue analysis. By using amulti-tone sinusoid waveform, the implemented system was capable ofperforming impedance characterisation from 1 kHz to 80 kHz with aminimum resolution of 1Ω. The system was verified first using anelectronic dummy model (metal plate), and subsequently with a biologicalsample (a piece of rib-eye steak under controlled temperatureconditions).

The measured results demonstrated that the instrument achieved a maximum2% error, a linearity of 0.1%, and a power consumption of 736.7 mW.

The designed instrument was compared with measurement results obtainedusing a commercially-available Agilent E4980A Precision LCR meter. Theimplemented system achieved similar performance in terms of relativeimpedance and reaffirmed the feasibility of the present technique. Asproof of concept, it has been shown that the design is versatile todifferent bioimpedances. With adjustable gain and configurable waveform,the present technique can be used on various tissues and conductivesolutions with various impedance ranges.

SUMMARY

The ability to acquire real-time diagnostics of brain tissueintraoperatively represents a key goal in the field of brain tumourneurosurgery. This can greatly enhance the precision, extent andeffectiveness of key surgical procedures such as those performed forbrain tumour resection and biopsy. To achieve this requires a miniature,handheld tool which can perform intraoperative in situ, in-vivocharacterisation of different types of tissues, e.g. normal brain tissueversus tumour tissue. In the present work we have explored thefeasibility and requirements of implementing a portable impedancecharacterisation system for brain tumour detection. We have proposed andimplemented a novel system based on PCB-based instrumentation using, forexample, a square four-electrode microsurgical probe. The demonstratedsystem uses a digital-to-analogue converter to generate a multi-tonesinusoid waveform, and a floating bi-directional voltage-to-currentconverter to output the differential stimulation current to one pair ofelectrodes, in each of a plurality of electrode switchingconfigurations. The other pair of electrodes in each electrode switchingconfiguration are connected to a sensing circuit based on aninstrumentation amplifier. The recorded data is pre-processed by themicro-controller and then analysed on a host computer. To evaluate thesystem, tetrapolar impedances were first recorded from a number ofdifferent electrode configurations to sense pre-defined resistancevalues. The overall system consumed 143 mA current, achieved 0.1%linearity and 15 μV noise level, with a maximum signal bandwidth of 100kHz. Initial experimental results on tissue were subsequently carriedout, including on a piece of rib-eye steak. Electrical impedance maps(EIM) and contour plots were then reconstructed to represent theimpedance values in different tissue regions.

Thus, a handheld electrical ‘tumour identification’ probe has beendeveloped which passes an electrical current through biological tissuewhile concurrently measuring the resistance to the flow of currentproduced by the tissue, i.e. the bioimpedance of the tissue. Bycharacterising this bioimpedance in real-time, the probe enables tissueidentification to differentiate normal brain tissue from abnormal braintissue, i.e. brain tumour tissue. The probe has been embodied as aminimally-invasive neurosurgical tool, e.g. for use in microscopic andendonasal endoscope assisted neurosurgery. The latter epitomises minimalaccess surgery necessitating the use of light, thin, long instrumentswhich can be easily manipulated, even with the restricted accessprovided by a single nasal passage.

Modifications and Alternatives

Detailed embodiments and some possible alternatives have been describedabove. As those skilled in the art will appreciate, a number ofmodifications and further alternatives can be made to the aboveembodiments whilst still benefiting from the inventions embodiedtherein.

Notably, in the above embodiments, the current source is primarilydescribed as being a voltage controlled current source, driven by avoltage waveform (generated by a voltage waveform generator). However,in alternative embodiments the current source may directly generate astimulation current for driving the electrodes, with the current sourcebeing driven by a current waveform generator. The current waveformgenerator may for example comprise a digital-to-analogue converterconfigured to receive a predefined stimulation waveform from which thecurrent waveform is generated. As in the case of the voltage waveform,such a current waveform may comprise a mix of a plurality of differentfrequencies, and be of substantially equal magnitude at each of theplurality of different frequencies.

Optionally the above-described probe 10 may be wireless, facilitatingunencumbered manipulation of the probe by the surgeon. However, it mayalternatively be connected to the control and analysis system by acable.

Optionally the above-described probe 10 may further comprise a pressuresensor, for measuring the contact pressure between the electrodes 20a-20 d and the tissue being tested. Contact pressure has been found tohave an effect on the impedance measurements, and consequentlymeasurements of the contact pressure obtained using the pressure sensormay be used to normalise the impedance measurements, thereby improvingthe accuracy of the impedance measurements.

Optionally the above-described probe 10 may further comprise, at thedistal end of the elongate body, a blood oxygen sensor (e.g. an opticalsensor to measure peripheral oxygen saturation (SpO₂)), for measuringthe blood oxygen level of the tissue being tested. This may be used tonotify the surgeon that a blood vessel is present within or near thetissue being tested. Accordingly, the surgeon may take suitable measuresbefore cutting out a tumour from the tissue in question, for example.

Optionally the above-described probe 10 may be incorporate anaccelerometer or inertial sensor to sense the angle of inclination (i.e.tilt) of the probe. This may be used to alert the surgeon if theyinadvertently change the angle of inclination of the probe to such anextent that that it risks causing injury to the patient, for example.

REFERENCES

-   [1] DeAngelis, L. M., 2001. Brain tumors. New England Journal of    Medicine, 344(2), pp. 114-123.-   [2] Khan, S., Mahara, A., Hyams, E. S., Schned, A. and Halter, R.,    2015, March. Towards intraoperative surgical margin assessment and    visualization using bioimpedance properties of the tissue. In    Medical Imaging 2015: Computer-Aided Diagnosis (Vol. 9414, p.    94141C). International Society for Optics and Photonics.-   [3] DePaoli D., Lemoine E., Ember K., Parent M., Prud′homme M.,    Cantin L., Petrecca K., Leblond F., Coto DC., 2020. Rise of Raman    Spectroscopy in neurosurgery: a review. Journal of Biomedical    Optics, 25(5).-   [4] Morimoto, T., Kimura, S., Konishi, Y., Komaki, K., Uyama, T.,    Monden, Y., Kinouchi, D. Y. and Iritani, D. T., 1993. A study of the    electrical bio-impedance of tumors. Journal of Investigative    Surgery, 6(1), pp. 25-32.-   [5] Faes, T. J. C., Van der Meij, H. A., De Munck, J. C. and    Heethaar, R. M., 1999. The electric resistivity of human tissues    (100 Hz-10 MHz): a meta-analysis of review studies. Physiological    measurement, 20(4), p.R1.-   [6] Chauveau, N., Hamzaoui, L., Rochaix, P., Rigaud, B.,    Voigt, J. J. and Morucci, J. P., 1999. Ex vivo discrimination    between normal and pathological tissues in human breast surgical    biopsies using bioimpedance spectroscopy. Annals of the New York    Academy of Sciences, 873(1), pp. 42-50.-   [7] Hu, S., Kang, H., Baek, Y., El Fakhri, G., Kuang, A. and    Choi, H. S., 2018. Real-time imaging of brain tumor for image-guided    surgery. Advanced healthcare materials, 7(16), p.1800066.-   [8] Latikka, J. and Eskola, H., 2019. The resistivity of human brain    tumours in vivo. Annals of Biomedical Engineering, 47(3), pp.    706-713.

1. Apparatus for discriminating between tumour tissue and non-tumoroustissue in real-time, the apparatus comprising: a handheld bioimpedanceprobe having an elongate body and at least four stimulator electrodesmounted on a distal end of the elongate body, the electrodes beingarranged to be held against a region of tissue in use; a current sourceconfigured to generate a stimulation current; a voltage sensor; amultiplexer coupled between the current source, the voltage sensor andthe stimulator electrodes and configured to changeably switch between aplurality of switching configurations, wherein, in each switchingconfiguration, a first two of the electrodes are connected to thecurrent source, and a second two of the electrodes are connected to thevoltage sensor, the electrodes that constitute the first two electrodesand the electrodes that constitute the second two electrodes changingfrom one switching configuration to the next; and processor-controlledcircuitry configured to: control the switching configuration of themultiplexer; control the generation of the stimulation current by thecurrent source and the application of the stimulation current to thefirst two electrodes of each switching configuration, such that, in use,the stimulation current flows through the tissue between the first twoelectrodes; control the measurement, by the voltage sensor, of thevoltage between the second two electrodes of each switchingconfiguration, across the tissue in use; determine, based on the appliedcurrent and the measured voltage for each switching configuration, ameasure of relative impedance of the tissue for each switchingconfiguration; and supply such impedance measurements as output data toa data analyser to enable real-time discrimination of the tissue to beperformed, based on the impedance measurements.
 2. The apparatusaccording to claim 1, wherein the current source is a voltage controlledcurrent source, and the processor-controlled circuitry further comprisesa voltage waveform generator configured to generate a voltage waveformand to supply the voltage waveform to the current source; optionallywherein the current source further comprises a high pass filterconfigured to remove DC offset from the voltage waveform and to convertthe voltage waveform to the stimulation current; optionally wherein thevoltage waveform comprises a mix of a plurality of differentfrequencies, and optionally wherein the voltage waveform hassubstantially equal magnitude at each of the plurality of differentfrequencies; optionally wherein the voltage controlled current source isprovided on a front-end printed circuit board or integrated circuitwithin the probe.
 3. (canceled)
 4. The apparatus according to claim 1,further comprising a current waveform generator configured to generate acurrent waveform for directly driving the current source; optionallywherein the current waveform comprises a mix of a plurality of differentfrequencies, and optionally wherein the current waveform hassubstantially equal magnitude at each of the plurality of differentfrequencies.
 5. The apparatus according to claim 2, wherein the voltagewaveform generator comprises a digital-to-analogue converter or a DirectDigital Synthesis module configured to receive a predefined stimulationwaveform from which the voltage waveform is generated; optionallywherein the stimulation waveform is stored in the processor-controlledcircuitry; optionally wherein the digital-to-analogue converter isprovided on a microcontroller unit platform.
 6. The apparatus accordingto claim 4, wherein the current waveform generator comprises adigital-to-analogue converter or a Direct Digital Synthesis moduleconfigured to receive a predefined stimulation waveform from which thecurrent waveform is generated; optionally wherein the stimulationwaveform is stored in the processor-controlled circuitry; optionallywherein the digital-to-analogue converter is provided on amicrocontroller unit platform.
 7. (canceled)
 8. (canceled)
 9. (canceled)10. The apparatus according to claim 1, wherein the voltage sensorcomprises an amplifier; optionally wherein the voltage sensor comprisesan instrumentation amplifier or a differential amplifier; optionallywherein the amplifier is provided on a front-end printed circuit boardor integrated circuit within the probe.
 11. (canceled)
 12. (canceled)13. The apparatus according to claim 10, wherein theprocessor-controlled circuitry further comprises an analogue-to-digitalconverter configured to receive and sample a voltage signal from theamplifier and thereby generate digital voltage data; optionally whereinthe processor-controlled circuitry further comprises a Fast FourierTransform processor configured to receive the digital voltage data fromthe analogue-to-digital converter, and to convert time-domain data intofrequency-domain data and thereby extract the instantaneous magnitude ofthe voltage data for each of a plurality of different frequencies in thestimulation waveform; optionally wherein the analogue-to-digitalconverter is provided on a microcontroller unit platform.
 14. (canceled)15. The apparatus according to claim 1, wherein the multiplexer isconfigured to cyclically switch between each of the plurality ofswitching configurations.
 16. The apparatus according to claim 1,wherein the processor-controlled circuitry comprises a microcontroller;and/or wherein the data analyser comprises a personal computer, a tabletcomputer or a smartphone; and/or wherein the electrodes are spherical orhemispherical; and/or wherein the electrodes are spring-loaded. 17.(canceled)
 18. (canceled)
 19. (canceled)
 20. (canceled)
 21. (canceled)22. The apparatus according to claim 1, wherein the distal end of theelongate body comprises a telescopic shaft on which the electrodes aremounted.
 23. The apparatus according to claim 1, wherein the probefurther comprises an adjustable handle member at a proximal end of theelongate body.
 24. The apparatus according to claim 23, wherein thehandle member is pivotally coupled to the elongate body.
 25. Theapparatus according to claim 24, wherein the handle member is pivotallyand retractably coupled to the elongate body by means of a linkagemechanism comprising a first joint mounted on or in the handle member, asecond joint mounted on or in the elongate body, and a connecting rodthat extends from the first joint to the second joint and passes throughat least one of the first and second joints to an adjustable extent,wherein at least one of the first and second joints comprises aball-and-socket joint to enable rotation in three dimensions.
 26. Theapparatus according to claim 25, wherein the second joint comprises aball-and-socket joint and the rod extends through the second joint to anadjustable extent; and/or wherein the first joint comprises aball-and-socket joint and the rod extends through the first joint to anadjustable extent.
 27. (canceled)
 28. The apparatus according to claim25 wherein, in the or each ball-and-socket joint, the surface of therespective ball part and/or the surface of the respective socket isadapted to hold the rotational position of the ball part relative to thesocket in a position as set by the user.
 29. The apparatus according toclaim 1, wherein the probe further comprises an operation button mountedon the elongate body, operable to activate the processor-controlledcircuitry; and/or wherein the probe further comprises depressions on theelongate body, for receiving the user's fingertips in use; and/orwherein the probe is wireless.
 30. (canceled)
 31. (canceled)
 32. Theapparatus according to claim 1, wherein the probe further comprises apressure sensor, for measuring the contact pressure between theelectrodes and the tissue in use; and/or wherein the probe furthercomprises a blood oxygen sensor at the distal end of the elongate body,for measuring the blood oxygen level of the tissue in use; and/orwherein the probe further comprises an accelerometer or inertial sensorto sense the angle of inclination of the probe.
 33. (canceled) 34.(canceled)
 35. A handheld surgical tool comprising an elongate body andan adjustable handle member that is pivotally coupled to the elongatebody.
 36. The tool according to claim 35, wherein the handle member ispivotally and retractably coupled to the elongate body by means of alinkage mechanism comprising a first joint mounted on or in the handlemember, a second joint mounted on or in the elongate body, and aconnecting rod that extends from the first joint to the second joint andpasses through at least one of the first and second joints to anadjustable extent, wherein at least one of the first and second jointscomprises a ball-and-socket joint to enable rotation in threedimensions; optionally wherein the second joint comprises aball-and-socket joint and the rod extends through the second joint to anadjustable extent, and/or wherein the first joint comprises aball-and-socket joint and the rod extends through the first joint to anadjustable extent; optionally wherein, in the or each ball-and-socketjoint, the surface of the respective ball part and/or the surface of therespective socket is adapted to hold the rotational position of the ballpart relative to the socket in a position as set by the user. 37.(canceled)
 38. (canceled)
 39. (canceled)
 40. A method of discriminatingbetween tumour tissue and non-tumorous tissue in real-time, using theapparatus according to claim 1 to 34.